Fiber reinforced polymeric resin composite materials are now widely used due to their outstanding strength-to-weight characteristics. Where it is desired to maximize these characteristics, carbon/carbon composite materials have been formed of carbon fibers such as those derived from PAN or pitch bonded by a matrix of pyrolytically formed carbon formed by pyrolysis of liquid resin impregnate or solid resin prepregnate or chemical vapor deposition or chemical vapor infiltration. While basic technology for the formation of such carbon/carbon composite materials has been around for a considerable period of time, it is currently being researched intensively as the need for the outstanding performance characteristics of such composite materials becomes more widely recognized.
Currently, structural components of such composite materials are joined one to another or to structural composites of, for example, an airframe, employing other materials such as conventional metallic fasteners or adhesives. Conventional mechanical fasteners of metal are unsatisfactory for several reasons. They are subject to a weight penalty and are susceptible to galvanic corrosion. Vibrations encountered during normal flight conditions and severe loading as experienced in storms or emergency maneuvers may result in failure of the fastener to the composite structure joint. Where such carbon/carbon composite materials are to be exposed to extremes of temperature, the difference in coefficient of thermal expansion between such conventional mechanical fasteners and that of the carbon/carbon composite material leads to undesired compromises or under utilization of the properties of the carbon/carbon composite material or premature failure of such joint or limits the service conditions to which the combination can be exposed. While adhesives have been employed to join such carbon/carbon composites, such adhesively bonded joints cannot readily be disassembled for service and maintenance.
While attempts have been made to solve the aforestated deficiencies, using composite plastic fasteners, these earlier efforts have not been widely adopted due to economic or technical shortcomings.
Exemplary of these earlier efforts are the following U.S. Patents:
______________________________________ Patent No. First Named Inventor ______________________________________ U.S. Pat. No. 3,495,494 A. L. Scott U.S. Pat. No. 4,478,544 Strand U.S. Pat. No. 2,306,516 Zahn U.S. Pat. No. 4,389,269 Cooper U.S. Pat. No. 4,265,981 Campbell ______________________________________
Scott discloses a threaded plastic member, having a glass fiber reinforced thread in which a plurality of resin impregnated glass fiber reinforcing filaments are disposed in serpentine manner throughout the cross section of the thread and extending longitudinally of the axis of the threaded member. The member is manufactured using a precision mold having a cavity complementary to that of the member to be formed.
Strand discloses a reinforced plastic rivet formed of carbon fibers encapsulated in an incompletely polymerized thermal resin matrix which in use is heated to soften the resin prior to upsetting of the rivet and full polymerization of the matrix. Strand's rivet is not threaded and has the disadvantage of needing to be stored prior to use in a controlled low temperature environment to prevent premature setting of the resin.
Zahn discloses use of a parting medium or membrane such as rubber over a threaded fastener which functions as a pattern to manufacture a hollow casting mold.
Cooper discloses a sport racket frame construction in which a resin impregnated tow is wound about part of a braided tow tube and thereafter a second braided tow tube is placed thereover to form an assembly that is internally pressurized and heat cured.
Campbell discloses impact resisting composites which may comprise multiple parallel filaments helically wrapped by a continuous multiple filaments or strips and embedded in a matrix material.
Carbon/carbon composite mechanical fasteners have been formed by machining them from larger blocks of carbon/carbon material.
While an exhaustive search has not been conducted, it is evident from the foregoing that a need remains for a threaded composite fastener suitable for use with carbon/carbon composite panel materials or structural members. A composite fastener which may be made economically in the absence of expensive molds is highly desired. A fastener which exhibits physical characteristics similar to modern composite materials such as those employed in aerospace applications and in harsh chemical environments is needed.